If your first attack goes from the right stance, it will take more time to hit the enemy even if you are moving left and doing all the same while spamming as usual. On a video you can see that attacks from the left stance reaching the target slightly faster.This isn't the stance system, that's just basic footwork. The stance system would be positioning right stance, which puts your right foot forward, and you have a slightly faster animation from a right swing. Moving left while swinging right does position your weapon closer - this is what I said - but it isn't coming from the stance system, it's coming from you literally moving your body closer to the opponent.
Once again, left stance is when you are moving to the left and your right hand is closer to the enemy, and right swings from that stance seem to be a bit faster